In introductory mechanics, the momentum of a particle is its mass times its velocity. In electrodynamics, the momentum of a field is proportional to the cross-product of the electric field with the magnetic field. In special relativity, momentum is generalized to four-momentum.

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Derivative of the action integral [closed]

I need to find the partial derivative of the action $S$ with respect to the generalized coordinate $q(t_f)$ and according to my textbook, it should equal the generalized momentum $p(t_f)$. I ...
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2answers
57 views

Why time of flight remains same for a projectile even though collision takes place?

Why time of flight remains same for a projectile even though collision takes place ? Suppose a ball is projected with some velocity V with some angle θ the the time of flight is T. Now if another ...
3
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4answers
317 views

Conservation of momentum in a baseball

Conservation of momentum: A thought experiment. A baseball is placed on top of a baseball holder, the kind used to train young batters. A batter hits the stationary ball perfectly horizontal, sending ...
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2answers
59 views

How can make myself sure that I can apply Conservation of Momentum in a system?

How do I know I can apply Conservation of Momentum in the System ? And What happens if there is a Impulse in the system?
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2answers
49 views

Stored Energy in My Badge Reel Finds Equilibrium With Centrifugal Force?

Probably a most horrible question title, please respond with suggestions for a better one. In the example of my badge reel, I grab hold of my badge itself and pull on the reel until the string is ...
3
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1answer
188 views

Area of phase space of Harmonic oscillator

We all know that the phase trajectory of an undamped linear harmonic oscillator is an ellipse. But when we calculate the area of the ellipse we find it does not depend of mass of the particle. Why is ...
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2answers
73 views

Why is it easier to drop on to a downslope?

On a bicycle, why is it easier to land from a drop or jump on a slope going downwards than landing on a flat surface or on an upslope? I've already heard answers such as "because that's how a bike ...
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0answers
60 views

Finding the momentum of a muon in $\pi\to\mu\nu_\mu$ [closed]

The $\pi$-meson's mass is 139.57 MeV, and it decays into a muon and a neutrino. The muon has a mass of 105.4 5MeV, and a proper lifetime of $2.197 \times 10^{-6}$. The neutrino can be treated as ...
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2answers
157 views

Problem regarding bullet penetration [closed]

Which property remains constant when we say that bullets are penetrating the wall? I mean is the resistive force always constant for a given wall (assumed stationary and immovable) irrespective of the ...
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4answers
190 views

Translational invariance implying diagonal representation in momentum space

I have just come across something in my reading of Peskin and Schroeder that claims that because a function, in this particular case a two-point correlation function, is translationally invariant, it ...
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1answer
206 views

Isolated system and conservation of momentum

I have a problem to understand isolated systems..If I have a ball and throw it upwards..then the momentum is not constant because the system is not isolated...and the reason is the external force from ...
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0answers
77 views

Four-momentum and Dirac equation in curved spacetime

Norm of four momentum in Minkowski spacetime is proportional to the square of rest mass as \begin{equation}|P|^2= P^\alpha \eta_{\alpha\beta}P^\beta= (E/c)^2 - p^2 = (mc)^2 \end{equation} While in ...
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83 views

Equating $\frac{dp}{dt}$ and $F$ at a hydraulic jump?

A journal I am reading about circular hydraulic jumps provides the equation and I quote: $H$= Depth after hydraulic jump, $h$= depth before hydraulic jump, $V$= velocity after hydraulic jump, $v$= ...
2
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3answers
94 views

Justification of $P_{\text{photon}}=E/c$ in derivation of $E=mc^2$

I recently was reading up on the derivation of $E=mc^2$. Now, I came across this derivation at this link. I noticed that several lines into the derivation they throw in the equation ...
3
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2answers
532 views

Estimate for energy dissipated by a damper/dashpot

I have a system with a mass $m$ attached to the end of a cable. The cable mass is assumed negligible. The cable is attached to the ground at the one end while the other, with the attached mass $m$, ...
1
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1answer
57 views

Is this treatment of the momentum operator in the Dirac formalism allowed?

I have a problem understanding a specific bit of Dirac notation. Take, as an example this derivation: I'm dubious about the step from line 3 to 4. When momentum operator acts on the momentum ...
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1answer
106 views

Do photons have no mass? [duplicate]

My Quantum Mechanics' teacher said today on the class that photons don't have mass. I was puzzled because I knew that photons have momentum. If a particle hasn't mass then its momentum sould be $0$ ...
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2answers
126 views

How force is transferred from one body to another

If there are 3 coins , namely 1 , 2 and 3 as in figure. When coin $1$ strike coin $2$ ,the coin $2$ passes the force to coin $3$ and the coin $3$ moves away. Case :1 How does this happen? What ...
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4answers
184 views

Why is force called the rate of change of momentum? [closed]

Why is force called the rate of change of momentum? If I push a wall I do exert a force but there is no movement; so is there force acting on the wall?
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1answer
128 views

Momentum and collisions [closed]

Two blocks of masses $m_1$ and $m_2$ connected by a spring of force constant $k$.The block $m_1$ is suddenly given a velocity $v_1$. Find the work done by the spring on both the blocks when it has ...
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1answer
137 views

Wavefunction interpretations in QM

From two-slit electron-interference experiment we can infer that there is a wave $\psi(x,t)$ that can be associated with electron. The amplitude at some point is the sum of amplitudes reaching that ...
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1answer
52 views

Physics Problem: Falling Rocket [closed]

A rocket, of mass $M = 40kg$, falls vertically with a speed of $60 m/s = v_0$ and explodes in two fragments of the same mass when it's at $H=2km$ from the ground. Immediately after the explosion one ...
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1answer
68 views

Momentum conservation in a small time interval

I recently solved a problem in which I used the "fact" that the momentum is conserved just before and just after a collision between two (or maybe more) objects but I am not sure whether this is true ...
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2answers
109 views

Conservation of momentum - finding the angle between broken parts

Let a stationary block explodes into 3 equal pieces .The speeds are also equal which is $v$. If I am asked to determine the angle between the broken pieces that are moving then how to deal with this ...
3
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1answer
87 views

If a photon doesn't necessarily travel in a straight line, doesn't it defy the law of cons. of momentum?

I just finished reading Richard Feynman's lectures on Quantum Electrodynamics (QED: The Strange Theory of Light and Matter) and it fascinated me. However, there's an unanswered question I have from ...
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2answers
198 views

Light and momentum question? [duplicate]

Each photon of light bulb carries momentum. Why does the light bulb not recoil from conservation of momentum?
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1answer
330 views

Water bottle rocket: Where does the energy go without water?

In Portland's OMSI there is a hands-on water bottle rocket station. (https://www.youtube.com/watch?v=cdtmVY76_PQ). The rockets are normal PET bottlers. The visitors fill their bottle with an amount of ...
3
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7answers
484 views

Why isn't momentum conserved in this pulley problem?

I have some conceptual doubt about method of solving this problem. 24. A block of mass $m$ and a pan of equal mass are connected by a string going over a smooth light pulley as shown in figure ...
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2answers
107 views

Doppler shift from a transversely moving plane mirror

Below is the diagram of the question I have on the Doppler shift of a light emitted from a stationary light source $S$ at an angle $\theta_1$ toward a transversely moving plane mirror $O$ having ...
2
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2answers
127 views

Is it possible to jump by using only my arms?

We can see that basketball players use their arms to jump higher. Is it possible to lose contact with the ground by only moving my arms? I know that the calculations have something to do with ...
3
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1answer
367 views

Fourier Transforms of position and momentum space in Quantum Mechanics

Fourier transformations: $$\phi(\vec{k}) = \left( \frac{1}{\sqrt{2 \pi}} \right)^3 \int_{r\text{ space}} \psi(\vec{r}) e^{-i \mathbf{k} \cdot \mathbf{r}} d^3r$$ for momentum space and ...
7
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2answers
230 views

What canonical momenta are the “right” ones?

I'm doing some classical field theory exercises with the Lagrangian $$\mathscr{L} = -\frac{1}{4}F_{\mu \nu}F^{\mu \nu}$$ where $F_{\mu \nu} = \partial_\mu A_\nu - \partial_\nu A_\mu$. To find the ...
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7answers
394 views

If we attach a fan at the end of a boat and switch it on, will the boat move? [duplicate]

I've been across a lot of questions like these, but I'm never quite able to get them. In this question, I reasoned that if I consider the boat and the fan to be a system, then there is actually no ...
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1answer
97 views

Terminal velocity of a raindrop

I have solved the question and got the answer , but I do not understand why will the raindrop attain a terminal velocity.Without any resistive forces why does it attain a terminal velocity?
3
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4answers
271 views

Is there difference in force when the height increases?

Consider a man with mass 50kg. When he jumps from a 2 meter height, the total force is $F=ma$ ie (mass * gravity), but nothing happens to him. When he jumps from a 50 meter height, the total force ...
3
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1answer
90 views

4 momentum in particle physics, collision of positron and electron

If I have a positron striking an electron at rest to create 2 pions( + and -) and I want to calculate the minimum kinnetic energy that the electrons can possess to create these pions, then the created ...
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0answers
52 views

Conservation of Mometum in integral form

Water is pumped from one reservoir into a another. The pipe expands after a lenght of $L/2$ to a diameter of $d$. Given: $\dot{V}_p, \rho_w, d, \eta, L, p_p$ The previos tasks allowed ...
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1answer
143 views

Dot Product Force

Konopinski's "What the electromagnetic vector potential describes" (Gaussian dimension) equation (3): $$\frac{d}{dt}[M\vec{v}+(q/c)\vec{A}]=-\nabla q[\phi-(\vec{v}/c)\cdot\vec{A}].\tag{3}$$ contains ...
2
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3answers
156 views

What's faulty in my reasoning about energy and momentum in this problem?

The question (from Sparknotes SAT Physics): An athlete of mass 70.0 kg applies a force of 500 N to a 30.0 kg luge, which is initially at rest, over a period of 5.00 s before jumping onto the ...
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2answers
62 views

How is Linear Momentum different from Thrust?

I know both theories are different in a complex way, but how them differ from the first ideas of movement? I cant really tell the difference... Thanks!!
3
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3answers
326 views

Why Can a Skydiver Hit the Ground and Be Killed? [duplicate]

This is a follow on question from Physics SE Question "Can a Skydiver Land On a Large Slide and Survive?". User Steeven gives this answer here. User Dargscisyhp asks: What is it exactly that ...
54
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6answers
6k views

Can a Skydiver Land On a Large Slide and Survive?

Please forgive my lack of artistic ability, but here's my question: Consider that a skydiver, without using his parachute, were to fall exactly parallel to a giant curved slide that starts at ...
0
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1answer
59 views

An Electron Chasing Another

An electron is held in place in deep space. Another electron approaches with speed $v_0$. When the approaching electron is a distance $r_0$ away from the first electron, the first is set free. The ...
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2answers
124 views

How did physicists arrive at conclusion that the product of mass and velocity is equal to momentum?

How did physicists arrive at conclusion that the product of mass and velocity is equal to momentum? What is the intuition behind $p=mv$? I had trouble finding any sources that state the actually ...
0
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3answers
84 views

Why can you turn on your bike without adding energy and still be moving?

There's a physical effect that I can't seem to figure out. When you are biking (on a bicycle), you have some speed. Then let's say you stop petaling and make a 90º turn to the right. You slow down, ...
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1answer
74 views

Rocket velocity during fuel burn [closed]

I know the formula for the velocity of a rocket after the on board fuel has been used up: $$ \Delta v = v_{ex} \ln\left( \frac{m_i}{m_e} \right) - gt $$ where: $v_{ex}$ is the exhaust velocity ...
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0answers
62 views

How to solve this energy problem using trends related to impulse and momentum? [closed]

The question runs a 1kg block moves with a speed of 10 m/s. It strikes a spring that has a spring constant of 25 N/m. Determine the maximum compression of spring. The energy way of solving ...
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3answers
214 views

Why the nonexistence of a “one sentence layman phrase” for the de Broglie relation $p=\hbar k$? [closed]

(My question seems most likely will be considered a duplicate of OP (and possibly 1, 2, 3), but it turns out to be WAY TOO LONG as a comment in OP, and the system has deleted the corresponding chat ...
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1answer
64 views

How is the kinetic energy of an object in collision converted to work done in deforming itself?

Usually, in a perfectly inelastic collision, maximum amount of KE is lost. I guess it depends on the rigidity of that object collision if any KE at all will be converted to work done to deform. ...